An antenna is one of the most important front-end passive components of a communications device. The antenna plays a very important role in performance of a communications product. Currently, an existing slot array antenna uses rows of through-holes provided on a surface of the slot array antenna to form a side wall of a rectangular waveguide, so that functions of a conventional rectangular waveguide are implemented. However, the antenna uses a serial feed. Due to constraints of the serial feed, bandwidth of the antenna is inversely proportional to a quantity of slots of each waveguide. Therefore, the antenna has narrow bandwidth, and cannot meet a requirement of a system for wider bandwidth.